WhitakerAudio J C Whitaker 20 W Stereo Audio Amplifier, Руководство пользователя, Страница: 153 / 194

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20 W Stereo Audio Amplifier
6.2.3 Power Management Expansion Board Adjustments
The power management expansion PWB works with the power management board to provide
additional functionality for the system, specifically: 1) auto-off based on an absence of output at
the speaker terminals, and 2) bias voltage monitoring. The following adjustments should be made.
– Set R402 and R408 for center of travel. Apply power to the amplifier. Connect a voltmeter
between ground and pin #2 of CONN402. Leave CONN402 connected; voltmeter probe
access can be made via the socket pin.
– Connect an audio source to the right and left channels. Program material is recommended,
rather than a tone generator.
– Turn both volume controls fully counterclockwise. Monitor the voltage on pin #2 of
CONN402. The voltage will slowly build up from 0.1 V. Turn the right channel volume
control clockwise so the program material is at a listenable level. The voltage on pin #2
should decrease to 0 V. Note that some delay is normal (about 30 seconds).
– Turn the right channel volume control fully counterclockwise. Note that after a short
delay, the voltage on pin #2 will begin increasing. Turn the left channel volume control
clockwise to a a listenable level. The voltage at pin #2 should decrease to zero.
– R402 and R408 can be adjusted for sensitivity on the right and left channels, respectively,
if desired. A center position is usually a good starting point, however.
– Run the amplifier with no input to check the auto-off circuit. The amplifier should shut
down approximately one hour after program material is removed. If the amplifier does not
shut down as it should, set R402 and R408 back (counterclockwise) 1/4-turn.
It may be noticed during use of the amplifier that with certain inputs, the auto-off circuit will
not shut the amplifier down. This is typically caused by residual noise from the input source.
Turntable sources are sometimes challenging since the noise floor for a turntable may be
considerably higher than for other inputs, such as a tuner or personal entertainment device. The
susceptibility of the silence detector circuit to noise can be determined as follows:
• Set R402 and R408 as described previously. Leave the Volume controls for each channel
in the position identified as a listenable level.